The present invention relates to a modular electronic supply device for a discharge lamp that may be used in particular for an outside lighting system or a system for illuminating an industrial building.
In the field of outside lighting, it is known, for example from EP-A-0 933 979, to use an electronic supply device, sometimes called xe2x80x9celectronic ballastxe2x80x9d, for an arc lamp such as a fluorescent tube, a sodium vapour lamp, a metal halid lamp or an equivalent lamp. In the known systems, the ballast is generally arranged either in the luminaire or at the foot of a public lamp post. In this latter case, a conductor cable connects the ballast and its peripherals to the lamp, over the height of the lamp post which is generally between 5 and 20 meters. The starting voltage of a discharge lamp being of the order of 4000 volts, the electrical supply line of the lamp over the height of the lamp post must be able to resist such a voltage and its section must be provided to be relatively large. At the present time, there exist two large families of electronic ballasts: those which directly supply the lamp with high-frequency current, generally several tens of kilohertz, and those which supply the lamp with a so-called square-wave current. The ballasts belonging to the second square-wave family deliver a current whose frequency is generally of some hundreds of hertz. The inductance of the cable connecting the ballast to the lamp creates an impedance proportional to the frequency of the current that it conveys and this impedance may significantly affect the performances of the ballast, in particular in the case of high-frequency supply. On the other hand, the impedance of the cable considerably attenuates the starting pulse delivered by the ballast when the lamp is lit. These phenomena make it necessary to reduce the distance between the ballast and the lamp. It is not always possible to install the ballast in height in the lamp post due to the question of space requirement. Moreover, if a ballast presenting an insulation transformer were used, the lower part of the lamp post would in that case be traversed by the mains current, which would cancel the safety procured by the galvanic insulation.
Furthermore, systems for regulating groups of discharge lamps exist, in which the supply voltage of all the lamps is varied, this voltage being able to be D.C. These systems do not allow an individualized control of the lamps and/or the connection of temporary accessories or material, as the network conveys a variable D.C. voltage incompatible with the majority of this material. These known systems in which control is effected in voltage, render the use of a ballast downstream of the D.C. supply line necessary.
Similar limitations exist with the known system of U.S. Pat. No. 4,751,398 in which ballasts are mounted downstream of a single common supply, these ballasts having to generate the supply current of a lamp and be dedicated to that lamp.
The problems set forth hereinabove are also encountered in the systems for illuminating industrial buildings in which the supply devices must be grouped together near the lamps, in particular in the upper part of the superstructure of a hall.
It is a more particular object of the invention to overcome these drawbacks by proposing a supply device with galvanic insulation which may be used with different types of individually controlled discharge lamps, in particular lamps functioning with high-pressure sodium vapour and metal iodide lamps, and whose space requirement is adapted to its environment.
To that end, the invention relates to a supply device for discharge lamps, characterized in that it comprises, for each lamp:
a first module or current injection circuit comprising, inter alia, a high-frequency inverter delivering a current adapted to ensure stabilization of the discharge in the lamp, a high-frequency transformer providing galvanic insulation of this current with respect to a supply network, then a rectifier and a filter adapted to produce a direct current at the output of this module,
a second module or starter-converter circuit, installed near the lamp and adapted to generate, by periodic inversions of the sign of the direct current at the output of the first module or current injection circuit, an alternating current in square-wave form for supplying the lamp, and
a bifilar electrical link between the first module and the second module.
The modular nature of the device of the invention makes it possible to install the second module in the immediate proximity of the lamp, for example in the lantern of a lamp post or in a cable trough or path of an industrial hall, while the current injection module may be installed at a considerable distance, the length of the D.C. supply line not being a hindrance since its impedance does not interfere with the performances of the device. In practice, this line may present a length of several hundreds of meters without this length significantly affecting the performances of the system. The fact that the first module constitutes an insulated source of current, in particular from the mains voltage at 50 or 60 Hz, makes it possible to render secure the different elements located downstream of this first module and, in particular the supply line, which, to a wide extent, eliminates the risks of electrocution associated with this type of equipment. The nature of current source of the first module enables it to perform the role of a ballast for the lamp that it supplies, thanks to the inversion of current obtained by the second module. In this way, it is unnecessary to provide a ballast in the proximity of each lamp. The current transiting in this D.C. supply line may be relatively weak, of the order of some amps, at a voltage of the order of some hundreds of volts. For these reasons, this line does not require particular precautions as to its insulation with respect to its environment.
According to advantageous but non-obligatory aspects of the invention, the device incorporates one or more of the following characteristics:
The second module or starter-converter circuit is compatible with lamps of different powers or of different types, while the first module or injection circuit is dedicated to a given power of lamps, the lamps being able to be of different types for a given power. The second module may therefore be mass-produced and installed by default in the lanterns of certain lamp posts or in the floodlights of certain industrial hall lamps, before the lamp is placed in position, the final choice of the lamp making it possible to associate a first module as a function of the exact type of the lamp.
The device comprises a third module or control circuit adapted to transmit information, particularly orders to start, to stop or to reduce power, to the first module or current injection circuit, as a function of instructions furnished by an outside system, while the exchange of information between the first and third modules takes place via a wireless, for example infra-red, link, in order to guarantee the galvanic insulation between these modules. The third module makes it possible to manage the possibly progressive start up, variation of power and interruption of the functioning of the lamp. This third module in fact makes it possible to transmit to the first module all types of instructions furnished by an outside system such as a system for remote-management of the lighting. This third module may be provided to receive information from the first module or current injection circuit concerning the functioning of the lamp and/or the modules and to transmit it to the outside system, which allows a return of information to that system. According to variant embodiments, the third module may be specific for one first module or injection circuit or associated with a plurality of first modules or injection circuits.
The first module or injection circuit comprises, inter alia, a first rectifier of the mains current supplying the high-frequency inverter associated with a power factor corrector and supplying the high-frequency inverter.
The second module or starter-converter circuit comprises four power transistors in a full bridge configuration and associated with an electronic control unit for starting and supplying the lamp with alternating current.
The second module or starter-converter circuit comprises a high-voltage transformer intended for starting the lamp.
In the case of a public lighting system comprising lamp posts, the lamp and the second module are installed in or in the immediate proximity of the lantern of the lamp post, while the first module is installed at the foot of this lamp post. In the case of an interior lighting system, the lamp may be installed in a deflector close to the ceiling of a building, the second module being housed in the vicinity of this deflector, in particular in a trough or path for cables supplying this lamp, while the first module is installed at ground level, in an easily accessible place.